Method of electroplating



April 17, 1951 J. M. KENNEDY ET AL METHOD OF ELECTROPLATING Original Filed Nov. 23, 1945 6 Sheets-Sheet l M wi mm km m NW mm Ina/animus. Jaimsfllifenneqq April 1951 J. M. KENNEDY ET AL 2,549,610

METHOD OF ELECTROPLATING Original Filed Nov. 25, 1945 6 Sheets-Sheet 2 April=l7, 1951 .1. M. KENNEDY ET AL METHOD OF ELECTROPLATING 6 Sheets-Sheet 5 Original Filed Nov. 23, 1945 deceased, 311/7 {)Cl 6 I N VEN TORSI Jamsflifemwdy. fIMOZdJL i 6 Sheets-Sheet 4 J. M. KENNEDY ET AL METHOD OF ELECTROPLATING April 17, 1951 Original Filed Nov. 23, 1945 April 17, 1951 J, M, KENNEDY ET AL 2,549,610

METHOD OF ELECTROPLATING Original Filed Nov. 23, 1945 6 Sheets-Sheet 5' I nveni/ons:

Patented Apr. 17, 1951 METHOD OF ELECTROPLATING James M. Kennedy and Harold J. Lee, Rome, N. Y., and Arthur P. Knight, deceased, late of Rome, N 15., by Norine E. Knight, executrix, Rome, N. Y.; said Kennedy, Lee, and Arthur P. Knight assignors to Revere Copper and Brass Incorporated, Rome, N. Y., a corporation of Maryland Original application November 23, 1945,-Serial No. 630,266. Divided and this application November 7, 1947, Serial No. 784,562

. 1 Oiir' invention relatesto methods of electroplating, the present application being a division of copending joint application of James Kennedy, Arthur P. Knight and Harold J. Lee, Serial Number 630,266, filed November 23, 1945, now Patent No. 2,506,794, dated May 9, 1950.

The invention has among its objects cladding the bottom portion of a cooking vessel or the like with a coating of metal such as copper, with provision for forming the coating with a marginal portion of gradually decreasing thickness as the edge of the coating is approached. From this aspect the invention constitutes an improvement in the method of electrodepositing the relatively thick copper coating according to the disclosure of applicants Patent 2,353,973, issued November 28, 1944.

The invention, however, will be best understood from the following description when read in the light of the accompanying drawings, the

scope of the invention being more particularly pointed out in the appended claims.

In the drawings: 7 Fig. 1 is a transverse section of plating apparatus according to the invention, corresponding to a section on the line i! of Figs. 6, '7 and 8; Fig. 2 is a section on the line 2--2 of Fig. 1; Fig. 3 is a fragmentary section, on an enlarged scale, on the line 33 of Fig. 6;

Fig. 4 is an elevation of a fragment of the I paratus according to Figs. 1, 6 and 7, with parts in elevation and parts broken away;

' Figs. 9 and 10 are more or less diagrammatic views illustrating the arrangement of carrier supports according to Figs. 1 to 8;

Figs. 11, 12 and 13 are, respectively, sections on an enlarged scale on the lines il-l I, 12-12 andit-lSofFigJl; M v

' Fig. 1.4 is a side elevation of the apparatus according to'Figs. l to 13, with parts omitted and parts broken away;

Fig. 15 is a section on the line i5l 5 of Fig. 14; Fig. 16 is a fragmentary transverse section of a modified form of apparatus, corresponding to Y Fig. 1, with parts omitted;

2 Claims.- (Cl. 204-) Fig. 17 is a fragmentary plan of the apparatus according to Fig. 16 illustrating a detail;

Fig. 18 is a fragmentary side elevation of the apparatus according to Fig. 16, with parts omitted, more or less diagrammatically illustrating a portion of the article carrier support;

Fig. 19 is a fragmentary transverse section of a further modified form of apparatus, corresponding to Fig. 1, with parts omitted;

Fig. 20 is a section on the line 2il20 of Fig. 19;

Fig. 21 is a fragmentary side elevation of the apparatus according to Fig. 1!), with parts omitted and parts broken away, more or less diagrammatically illustrating a portion of the article carrier support;

Fig. 22 is a fragmentary section, on an enlarged scale, of the lower corner portion of the vessel according to Fig. 2 showing an electrodeposited plating or coating applied thereto; and

gated tank 5, preferably formed of lead coated steel, is adapted to contain a body of electrolyte the upper surface level of which is indicated at L (Fig. 1). .As shown, in this electrolyte are immersed the lower portions of cooking vessels or like articles A, the bottom portions of which are to be clad with a relatively thick coating of metal such as copper.

The upper edges of the tank are shown as provided with longitudinally extending horizontal flanges 3 upon which, at each of opposite longitudinal sides of the tank, rests a strip 5 of insulating material such as fiber. Supported on these strips are bus-bars 1 preferably of -co-pper. For securing the bus-bars and insulatingstrips to the flanges are shown bolts 9 extending from the lower sides of the flanges through the strips 5 and ta ped into the bus-bars 1, the bolts being insulated from the flanges by the insulating bushings ll. Connected to the outer edges of the bus-bars l, as by brazing or welding, are cable lugs 3 to which are connected thev cables l5 and H for connecting the bus-bars to the opposite terminals, respectively, of the source of current supply.

As shown, connected to the inner edge of one of the bus-bars l. as by brazing or welding, are the up er ends of the downwardly directedportions is of bars having horizontal portions 2| submerged in the electrolyte. these horizontal portions extending transversely across the tank. As shown, the bars i9, 2! are supported on suitable brackets 23 carried by the side walls of the tank, which brackets are also preferably lead covered to render them inert with respect to the electrolyte. Carried by the horizontal portions 21 of each of the bars are shown a plurality of spaced anodes, herein two. These anodes, as illustrated, comprise annular trays 25, preferably formed of lead or other conductive material inert with respect to the electrolyte, which trays are filled with a mass 2'! of copper shot or the like forming a readily replenishable or renewable soluble anode.

The above mentioned trays 25 are shown as resting upon disks 29, preferably formed of copper and welded to the upper side of the bar portions 2|. As shown, each disk is formed with an upwardly projecting nipple 31 received in the opening of the annular tray 25. As illustrated, the nipple and disk are formed with an opening 33 which is continued to the underside of the bar portion 25. In the upper end of this opening is screw-threaded a nozzle 35 formed of hard rubber or other suitable insulating material, the edge of the nozzle overlying the edge of the annular tray 25 so that the nozzle secures it to the disk 29 in electrical contact therewith.

As shown, each nozzle 35 is provided with a group of upwardly directed openings 3? (Fig. 6) for projecting electrolyte upward toward the bottom of the vessel A, and with distributed radially directed openings 39 (Figs. 1 and 6) for projecting electrolyte in all directions radially of the bottom of the vessel. For supplying electrolyte under pressure to the nozzle, screw-threaded into the lower ends of the opening 33 is shown a pipe connection 4!, preferably formed of lead, which is connected by a length of rubber hose or conduit of other insulating material, to the outlet nipples of a lead pipe extending longitudinally of the tank. As shown (Fig. '7) this pipe has a portion 69 connected to the outlet of a motor driven pump 5! at the exterior of the tank, the inlet of the pump being connected to the tank by a pipe 53 so as to draw electrolyte therefrom and supply it to the pipe 3-9, in which way the electrolyte is circulated.

Supported on posts 55 (Figs. 1 and 3) carried by the bar portions 2| are ring members 5'1 having flanged radially extending portions 59, upon which latter rest annular metal shields 6i positioned between the anodes and the peripheral portions of the vessels. As shown, the exposed portions of the bar portions 2 i, disks 29, posts 55, ring members 57 and shields H are covered with a layer 63, of rubber or other insulating material, for protecting and insulating them from the electrolyte. As shown, the shield is removable so that shields with different size openings 5-3 may be substituted to accommodate vessels of different diameters.

The above described nozzles 35 and shields 64 are identical with those disclosed in the above mentioned patent, and are arranged dimensionally with relation to each other and the anode and vessel as therein shown and described, and serve the same purpose. Briefly, this purpose is by use of the nozzle to permit, in conjunction with the rotating vessel, a higher current density per unit of cathode surface and eliminate the possibility of quiescent spots in the electrolyte at the axial portion of the bottom of the tating vessel, while the shield causes the path travel of the plating current from the anode to the vessel progressively to increase from points opposite the inner peripheral edge of the annular shield to the edges of the surface being plated, hence to cause the value of the current and consequent rate of deposition progressively to diminish from points opposite the inner peripheral edge of the shield to the edge of the surfaces being plated as compared to what they would be were the shield omitted.

As shown, the vessels A are supported by carriers comprising the spaced bars 65 which are preferably formed of metal such as brass and are integrally connected at their ends by cross-bars 61. As shown, at the intermediate portions of the carrier are cross-bars 69 integrally formed with the bars 55. These bars 69 have depending portions H which are perforated for fixedly carrying elongated sleeves 13, in which latter are rotatably mounted vertical shafts 15. As shown, carried by the lower end of each shaft 15 is, a chuck for supporting the vessel A. The chuck, which is preferably formed of resilient sheet copper, has a bottom T1 to which the shaft '15 is joined, as by welding, and has side walls formed with V shaped splits 19 to form a circular series of spaced resilient prongs 8!, the latter engaging the lower portions of the side walls of the vessel for supporting it and detachably connecting it to the shaft 15. As shown, each shaft 1% is provided at its upper end with a bevel gear 83 meshing with a bevel gear 85 on a horizontal shaft 81 rotatably supported in bearings 89 on the carrier cross-bars 69. The shaft 81 is shown as connected by an insulating coupling 91 to an electric motor 93 for driving said shaft, the motor being supported on a plate 95 of insulating material carried at opposite ends by the side bars 65.

For energizing the motor 93 the plate 95 of insulating material which supports it carries a pair of downwardly projecting brushes 9'! connected by leads 98 (Fig. l) to the motor terminals. These brushes have contact portions S9 engaging the flat bar-like trolley wires Ifli extending longitudinally of the tank. As shown, these trolley wires are carried by brackets I03 supported by the adjacent side wall of the tank, insulating strips I65 being positioned between the wires and the brackets, these bars and strips being conveniently secured to the brackets in the same way as the bus-bars 1 and insulating strips 5 are secured to the tank flanges 3. The brushes 9'! are of a known type in which the contact portions 99 are yieldingly extensible relative to the body of the brushes so as to maintain contact with the trolley wires when the carrier is slightly raised, as will be hereinafter described. The trolley wires may be con nected to a suitable source of electromotive force by leads indicated at I01 (Fig. '7).

As shown, the bus-bar I at the left hand side of the, tank, as viewed in Figs. 1 and 6, is provided with raised portions in the form of plates I09, preferably of copper, of progressively increasing thickness from one end of the tank to the other, as illustrated in Figs. 8 and 9, these plates being secured to the bus-bar in any convenient way as, for example, by screws I ll (Figs. 11 and 12) or by welding or brazing, so that the plates will be in electrical communication with the bus-bar. As shown, the carrier is provided with a cross-bar I 13 having a depending portion 1 Hi adapted to rest upon these plates. This crossbar is integral with the carrier side bars 55, and as the cross-bars 69 are also integral with those side bars, and the shafts :5 are in electrical communication with the metal sleeves 13 supported '"For supporting the carriers at the side of .the

tank opposite the plates IDS is provideda horizontal rail I I5 coextensive with the length of the 'tank. This rail, as shown, is carried by spaced brackets IN, and on the rail are platesv Ht of insulating material, which plates are. positioned directly opposite the plates I89 and are of the "same thickness as the latter. The carrier cross- 'bar -6! adjacent the rail I ib has adepending portion I2I' similarto' the depending portion N4 of the cross-bar II3'at the opposite side of the tank, which depending portion I2! is adapted to "rest upon these plates I19.

Supported by each-of the brackets It! at opposite-sides of the tank is a rail I23 coextensive with the length of the tank. At eachend the carrier is provided with apair-of wheels I25 adapted to ride on these rail -When the carrier is moved off the plates I83 and I 59, these plates lifting the wheels on" the rails when the carrier is moved to position it on the plates. As a result the Wheels ride on the rails only when the carrier is being moved lengthwise of the tank from --one pairof these plates to the adjacent pair. As

Will be clear from Fig. 8, the rails I23 are up- -wardly inclined from, one end of the tank to the other so that the plates at each station Will raise me-rsion of the vessels A to be progressively decreased as they are progressively placed over different anodes by movingthe carrierlengthwise jections 135 at opposite Sides of the chain so as to engage with the body of the latter.

As shown. the chains I3I at opposite sides of the tank are each driven by a chain Hi3 (Fig. '7) having ,a sprocket wheel connection .with a common shaft I45, so that the chains I3I will be driven in unison. For driving the shaft I is provided an electric -motor I47 adapted to be connected in driving relation to the shaft through an electroemagnetically controlled clutch, the clutch elements of which latter are schematically indicated at 49 and the energizing winding at I5I. The clutch as shown is indicated in open position so that the chains I3! will be stationary while the articles are over the anodes. Conveniently the motor is connected to the clutch through a reduction gearing, the casing of which is indicated at I53. For intermittentlyenergizing and deenergizing the winding I5I of the clutch, so as intermittently to open and close the latter, is provided a synchronous motor schematically indicated at "I55, which vmotor slowly turns 'a disk i5! of insulating material connected to the motor through a reduction gearing the casing of which is indicated at I59. As shown, the disk is pro vided at its periphery with a segment iul of conductive material adapted intermittently to contact .with .a brush I53 connected to one terminal of the clutch energizing winding I5I, the

other terminal of which winding is connected to one side its of a line for energizing this winding. The other side It! of this line is connected to a brush I69 contacting with .a ring ill of conductive material carried by the disk "I51, which ring is connected by a lead I13 to :theconductive segment It! on the disk. As a result, when the diskis slowly rotated to cause the brush I63 to contact with the segment IBI the winding of the clutch will be energized wto cause the clutch to close, and, while it is of the tank to place them on different plates. The p heights of the upper surf-aces of the plates may I be readily varied by machining ofi those surfaces or by building them up or substituting differentplates, so asto compensate for settling or warping of the tank and for controlling the depth of v immersion of the vessels while over the respective anodes.

For moving the carriers lengthwise of the tank'- -the cross-bars B'i at opposite ends of the carrier are shown as provided with projecting bar-like members I29 formed of insulating material. Extending lengthwise of the rails is shown'a chain iti the upper run of which is positioned be neath these members. This chain is of usual construction except that pairs oiopposite side links '533 at spaced point along the chain'- have upwardly projecting portions I35 (Figs. 1, 4. and 14.) which are adapted to engage with the members 529 of the carriers When the chain is moved. By moving the chain intermittently it in this way is 'eifective to push thecarriers to position the ves- As illustrated, the chain passes around that they mayenter the spaces'between the proclosed, the motor I4? will move the chain to cause the carriers to be transferred from over one set of. anodes to the immediately adjacent set'. The angular length of the segment is so designed withrelation to the speed of the disk 55? that the chain will stop moving as soon as the carriers are placed above each set of an- For supplying the plating current is shown I a generator H5 the opposite terminals of which are connected by leads iii to the opposite busba'rs i, respectively. These bus-bars preferably are not continuous, but are formed in sections connected to the generator terminals in parallel so that the amount oi current carried by each section will be reduced. As indicated in Fig. '7,

"the adjacent ends of these sections are separated'by insulating blocks lls. As schematically shown in Fig. '7, the field winding of the generator is provided with a voltage control section l8! controlled by a'switch 33 adapted to be operated by a solenoid I connected in series relation with the winding I5I of the electro-magnetic clutch, so that when this latter winding is energized the solenoid will be simultaneously energized to cause the switch I83 to close and thus reduce the voltage "of "the generator to a low value. This provides that when the clutch is closed. to cause the carriers to be moved the plating current is substantially interrupted and will not be again establisheduntil the chain ceases to move, so that arcing will not-occur.

, As pointed; out inapplicantsipatent above-referred to, it is of importance, in plating the lower portion of a cooking vessel with a relatively thick layer of copper or other metal for distributing the heat applied to the vessel, to have the marginal portions of the plating gradually taper to a feather edge merging into the surface of the base metal. Although excellent results in these respects may be secured by use of the shield above mentioned, it has been found that improved results can be secured by gradually decreasing the immersion of the vessel as the plating operation is continued. For example, if the vessel A (Fig. 22) is initially immersed for a depth of about by gradually decreasing the depth of immersion to about A, the tapered portion is! of the plated layer !39 may be much more readily secured and its shape readily controlled. Various shapes of vessels may be readily plated in this way as, for example, the approximately square cornered vessel AA shown in Fig. 23, with which shape of vessel the Opening in the annular shield Si is preferably so designed as to cause the plating layer iSl to bulge considerably adjacent the corners of the vessel, as indicated at I93, so as to protect the plating from injury at the corners of the vessel during handling of the latter when subjected to use in the kitchen.

It has been found, for example, that in cladding a cooking vessel of the shape shown by Fig. 22 or 23 and of material such as stainless steel, aluminum, or iron requiring, or improved by, a copper cladding for distributing the heat, satisfactory results commonly will be secured with a cladding about 0.03" thick on the bottom of the vessel, and that a satisfactory tapered layer can be secured by causing the cladding to be plated in eighteen steps, each electrodepositing on the bottom of the vessel a layer about 0.0017" thick. With a current density of about 350 amperes per square foot of cathode surface and asulphuric acid electrolyte consisting of about by weight of sulphuric acid and by weight of copper sulphate such a layer may be deposited in about 5 /2 minutes. In this operation the vessels may be rotated at such linear speed'at the major diameter of the immersed portions as corresponds to about 250 R. P. M. for a vessel 7 inches in diameter. At this speed a thin film of electrolyte is drawn up the walls of the vessel for about above the normal electrolyte level, and due to the attenuation of this film the deposition of copper from it proceeds at a very slow rate as compared to the rate of deposition on the bottom of the vessel. This results in the metal deposited from the film merging into the surface on which it is deposited. It will be understood that by progressively decreasing the immersion of the article the marginal portion of the layer deposited on the vessel when it is over each anode will overlap with the marginal portion of the layer deposited when it is over the preceding anode. For example, if the depth of immersion is decreased in eighteen equal steps and the film is drawn up the walls of the vessel about 1% as above described, each layer will overlap the other about 0.04. So as to have the rate of deposition at each station approximately the same, the anodes preferably are positioned progressively at a higher elevation as the row of anodes progresses lengthwise of the tank, so as to have them in approximately the same relation to the bottom of the vessel as the depth of immersion of the latter is progressively decreased. In cladding the vessel according to Fig. 22, satisfactory results will be secured with with the current density, electrolyte concentration, and speed of rotation of the vessel, above mentioned, when the upper level of the copper shot in the anodes is spaced about 2 inches from the bottom of the vessel and the shield is spaced about 1 inch from the bottom of the vessel, the shield having an opening approximately 1 to 2 inches less than the diameter of the vessel, and with about 5 gallons of electrolyte per minute discharged through each nozzle, the radial openings 39 of the nozzle being about 1% inches below the bottom of the vessel.

In operation the carriers may be placed above the anodes at the first station in the tank, and may be removed from the anodes at the last station, by suitable conveyer means of a known type, these conveyer means preferably lifting the carrier by engagement with the projecting members I29 at each end thereof.

It will be understood that preliminary to the plating operation above described the vessel may be subjected to such treatment as is necessary to prepare it for such plating. For example, if the vessel is a stainless steel cooking vessel, it may be subjected to the preliminary treatment described in applicants above mentioned patent, namely, roughening the surface to be plated by an anodic treatment or otherwise, treating the roughened surface with electrolytically released hydrogen by making said surface a cathode in a non-metal bearing sulphuric acid electrolyte, and applying a fiash coating to the cathodically treated surface. These operations consume but a relatively short period of time, with the result that vessels will be ready to be placed in the plating tank above described about every 6 minutes.

The vessels may be loaded on the carrier before be readily performed. For example, a loaded carrier may be started about every 6 minutes through the apparatus for performing the preliminary treatment of the vessels, and substantially immediately upon the completion of the operation of depositing the fiash coating, that is to say about every 6 minutes, a loaded carrier may be placed at the first station in the plating tank, and then every 6 minutes the carrier may be moved to the next successive station in the plating tank, the carrier remaining at each station about 5 minutes. In this way a row of carriers will be maintained in the plating tank, the end carrier of the row being removed from the tank in this example every 6 minutes.

In the form of apparatus shown by Figs. 19 to 21, the wheels I25 of the carriers remain continuously 0n the rails 23, the raised plates I09 and H9 being omitted. In this modification the cross-bar H3 carries a brush I continuously in contact with the adjacent bus-bar 1. As shown, this brush has rigidly secured thereto bolts l9? screwed at their lower ends into the brush and slidably extending through openings I99 in the cross-bar, which openings they fit with sufiicient tightness to place them in electrical commun cation with the cross-bar so as to conduct current from the bus-bar to the carrier. As shown,

the brushes are maintained in contact with the bus-bar by springs 2M received in openings 293 r in the cross-bar and bearing at their lower ends against the brushes. As shown, the rails I23 are upwardly inclined from one end of the tank I to the other, so that the carrier as it is moved from one anode station to the other is progressively raised for decreasing the depth of immersion of the vessels.

In the modification shown by Figs. 16 tom the cross-bar H3 of the carrier permanently contacts with the adjacent bus-bar 'I, while the insulating plate '95 which, as shown in Fig. 1, supports the motor 93 and brushes 97, is provided with a downwardly projecting portion 295 which rests upon the adjacent bus-bar I, so that the carrier is supported on these two bus-bars. For raising the carrier as ittravels along the tank, so as to vary the depth of immersion, the two bus-bars I, as shown in Fig. 18, are upwardly inclined from one end of the tank to the other, being for this purpose supported on an insulating strip 291, which strip is like the insulating strip 5 of Fig. 1 exsept that it is of progressively increasing thickness as it extends from one end of the tank to the other.

In this last mentioned modification each'of the projecting members I29 at the opposite ends of the carrier is provided, on the side thereof engaged by the spaced pairs of projections I35 of the chain, with a block 209 adapted to be embraced by the adjacent pairs of projections when the latter engage with said member. This construction causes the projections on the chains to 7 hold the carriers against substantial endwise movement on the bus-bars I. For facilitating entry of the blocks 209 into the spaces between the chain projections I35 when the carriers are initially placed over the tank, the upper ends of said projections are shownat 2 as bent outwardly to form a flared opening between them.

It will be understood that within the scope of the appended claims wide deviations may be made from the forms of the invention herein described without departing from the spirit of the invention. I

We claim:

1. The method of electrodepositing, on the bottom and contiguous lower side wall exterior surfaces of revolution of a cooking vessel, a cop- 10 per coating which, on the side wall surface, is of progressively decreasing thickness as its upper edge portion is approached and merges as its upper edge into said surface, which method comprises electrodepositing the coating in successive steps, each for electrodepositing a thin layer of copper on said surfaces, by immersing only the bottom and lower side wall portions of the vessel in an electrolyte with its bottom opposed to an anode and with its axis positioned vertically, progressively decreasing the depth of immersion of the vessel for said steps, during each step axially rotating the vessel for drawing a film of electrolyte up the side wall surface above the level of the contiguous electrolyte a distance which is greater than the decrease in the depth of immersion of the vessel from the immediately preceding step and is less than the total decrease in immersion for the total number of steps, whereby the portions of the copper layers electrodeposited on the portions of the side walls in contact with said films during successive steps overlap, as do likewise the portions of said layers electrodeposited on the portions of said side walls below said films, with the upper edges of those portions of said layers at progressively decreasing distances from the bottom of the vessel.

2. The method according to claim 1 in which the anode is positioned below the bottom of the vessel approximately the same distance for each step.

JAMES M. KENNEDY. HAROLD J. LEE. NORINE R. KNIGHT, Erecut'rizc of the Estate of Arthur P. Knight, De-

' ceased. i

REFERENCES CITED The following references are of record inthe file of this patent:

UNITED STATES PATENTS Name Date Anthony Mar. 25, 1919 Merritt Mar. 30, 1920 Engelhardt et a1. Aug. 5, 1930 Number Plensler Dec. 6, 1938 Kennedy et al Nov. 28, 1944 

1. THE METHOD OF ELECTRODEPOSITING, ON THE BOTTOM AND CONTIGUOUS LOWER SIDE WALL EXTERIOR SURFACES OF REVOLUTION OF A COOKING VESSEL, A COPPER COATING WHICH, ON THE SIDE WALL SURFACE, IS OF PROGRESSIVELY DECREASING THICKNESS AS ITS UPPER EDGE PORTION IS APPROACHED AND MERGES AS ITS UPPER EDGE INTO SURFACE, WHICH METHOD COMPRISES ELECTRODEPOSITING THE COATING IN SUCCESSIVE STEPS, EACH FOR ELECTRODEPOSITING A THIN LAYER OF COPPER ON SAID SURFACES, BY IMMERSING ONLY THE BOTTOM AND LOWER SIDE WALL PORTIONS OF THE VESSEL IN AN ELECTROLYTE WITH ITS BOTTOM OPPOSED TO AN ANODE AND WITH ITS AXIS POSITIONED VERTICALLY, PROGRESSIVELY DECREASING THE DEPTH OF IMMERSION OF THE VESSEL FOR SAID STEPS, DURING EACH STEP AXIALLY ROTATING THE VESSEL FOR DRAWING A FILM OF 